1. Field of the Invention
This invention relates to novel xanthene compounds and to their use, e.g., as light-screening dyes in photographic products and processes.
2. Description of the Prior Art
It is well known that photographic film, and especially multicolor films, may and generally do vary from lot to lot, notwithstanding efforts to "repeat" previous films. Manufacturers of multicolor photographic films have developed a number of procedures to minimize the effects upon the final multicolor image of unavoidable variations in the manufacturing operations. These variations are reflected primarily in shifts in color balance as reflected in mismatching of the D log E curves of the individual red, green and blue exposures. Equipment used to coat multicolor films is highly precise but variations between intended coverage of silver halide and/or the dye image-forming materials do occur. Repeat batches of silver halide emulsions may, and usually do, vary in their photographic response. Individual layers may be dried to slightly different degrees. Films are stored for a period of time after coating to allow the films to "age", so that changes in sensitometry following coating have an opportunity to reach a plateau prior to sale. If the film is designed to be developed by a photofinisher or in a darkroom, processing of the exposed multicolor film is controlled within very narrow limits, typically within plus or minus a half degree of a prescribed temperature, in order to minimize sensitometric variations from film to film. Where the multicolor film is of the negative type, an opportunity to adjust the sensitometry occurs in printing the desired final positive image, during which operation the printing exposure may be appropriately color filtered.
The basic sources of sensitometric variations noted above exist also in multicolor diffusion transfer films, with the added complication that once the film is shipped, the sensitometric properties are essentially fixed. The opportunity for adjustment provided in darkroom processing, practically speaking, is unavailable for users of self-developing films. While professional and advanced amateur photographers may be skilled enough to utilize color correction filters to at least partially "rebalance" the color balance, ordinary users of the film would only be confused by such additional operations.
It is well known to use light-screening dyes in photographic elements. Such a dye may be incorporated as a filter dye in a light-sensitive emulsion layer(s) or in a layer coated over one or more light-sensitive emulsion layers or between two differently color-sensitized emulsion layers to modify the light record in the emulsion layer or to control the spectral composition of light falling on the underlying light-sensitive layer, or it may be incorporated as an antihalation dye in a non-light-sensitive layer positioned on either side of a support carrying the light-sensitive layer(s).
The dyes employed for these purposes, in addition to having the requisite spectral absorption characteristics for their intended use, should be photochemically inert, that is, they should not have any adverse effect on the properties of the light-sensitive emulsion layer(s), and also, they should be capable of being decolorized or removed during photographic processing so as not to leave stain in the processed photographic element. In photographic processes where the dye is removed by being dissolved in a processing solution, it is usually preferred that the dye also decolorize in order to avoid contamination of the processing solution and to prevent staining from residual dye in the processed light-sensitive element.
Though various classes of dyes have been proposed for use in antihalation and color correction filter layers, the dyes heretofore employed have not been altogether satisfactory. Some of the dyes tend to reduce sensitivity, fog or exert other adverse effect on the light-sensitive material. However, the major drawback of previously employed dyes is their tendency to cause stain due to incomplete decolorization or reversal of some of the decolorized form to the original colored form. For example, some classes of dyes rely on the presence of a reagent, such as, a sulfite for "bleaching", i.e., decolorization and unless the dyes are removed from the light-sensitive material during or after processing, their color may reappear in time.
Among the classes of light-screening dyes used previously are the triarylmethanes and xanthenes. For example, U.S. Pat. Nos. 1,879,537; 1,994,876; 2,350,090 and 3,005,711 disclose the use of fuchsone-type dyes in antihalation layers, and U.S. Pat. Nos. 3,406,069 and 3,615,548 are concerned with the metal chelates of fuchsone dyes as antihalation dyes. These and other types of triarylmethane dyes suffer from one or more of the drawbacks discussed above, and in particular, prior dyes of this type have been difficult to keep decolorized at the pH's normally encountered during processing subsequent to "bleaching" and in the final product. Xanthenes have been employed in antihalation layers that are removed during photographic processing. For example, U.S. Pat. Nos. 2,182,794; 2,203,767 and 2,203,768 disclose the use of rhodamine dyes in certain antihalation layers that are removed during processing in an acid bath or a plain water rinse bath depending upon the solubility characteristics of the particular layer.
Copending U.S. Patent Application Ser. No. 106,905 of James W. Foley, Louis Locatell, Jr. and Charles M. Zepp filed concurrently herewith is concerned with certain 3,6-bis-(N-indolinyl)xanthene compounds. These compounds find utility as photographic light-screening dyes and offer advantages over the light-screening dyes previously used because of their ability to decolorize completely and irreversibly to a substantially inert colorless product. Specifically, the dyes disclosed and claimed therein comprise xanthene compounds of the formula ##STR3## wherein X is ##STR4## wherein R' is alkyl; Y is an electron-withdrawing group and A is an anion.
The present invention is concerned with sulfo-substituted xanthene compounds of this type having improved properties.